In recent years, display devices employing organic EL elements have become widespread owing to characteristics of the organic EL elements such as a high visibility resulting from self-luminescence and an excellent shock resistance resulting from a fully solid-state structure.
According to a structure of an organic EL element, at least a light-emitting layer is disposed between a pair of electrodes (an anode and a cathode). Further, the organic EL element typically includes, between the light-emitting layer and the cathode, a functional layer (an electron transport layer, an electron injection layer) for supplying electrons to the light-emitting layer, a hole injection layer, a hole transport layer, and so on. Also, it is known that an excellent electron injection property is exhibited by functional layers made of an alkali metal or an alkaline-earth metal having a low work function.
Alkali metals and alkaline-earth metals that have a low work function react easily with impurities such as moisture and oxygen. For this reason, impurities degrade the functional layer that includes an alkali metal or an alkaline-earth metal. This exercises an adverse effect such as degradation of light emission efficiency and reduction of light-emitting lifetime of the organic EL element, and degrades storage stability. Also, contact between impurities and a cathode causes corrosion and degradation of the cathode. This can cause the same adverse effects described above.
In view of this problem, Patent Literature 1 discloses an organic EL element including an inorganic barrier layer between a hole injection layer and a hole transport layer, between the hole transport layer and a light-emitting layer, between the light-emitting layer and an electron transport layer, or between the electron transport layer and an electron injection layer (these layers are referred to as organic light-emitting medium layers in Patent Literature 1). The inorganic barrier layers are provided in order to prevent one or more of the organic light-emitting medium layers, which are formed subsequent to the corresponding inorganic barrier layers, from being degraded by impurities that are adsorbed onto surfaces of a remainder of the organic light-emitting medium layers, which are formed prior to the corresponding inorganic barrier layers (the impurities are referred to as a degradation factor in Patent Literature 1).